This invention pertains generally to the manufacture of semiconductors and more particularly to apparatus suitable for loading a susceptor and wafers supported thereby into and out of a reaction chamber.
One type of chemical vapor deposition system used in the production of semiconductors is a reactor having a horizontally extending tube defining a reaction chamber. Such reactors are utilized, for example, in the deposition of silicon dioxide, silicon nitride, polycrystal silicon, and epitaxial silicon films. Horizontal tube reactors have a high wafer capacity and rapid cycle time, and they are particularly suitable for high volume wafer production.
Heretofore, horizontal tube reactors have been loaded manually, and the susceptor and a quartz sled on which the susceptor is mounted are typically withdrawn from the quartz reaction tube onto a loading dock using a pushrod. Wafers are loaded onto the susceptor, and the susceptor and sled assembly is pushed back into the reaction tube to a predetermined depth to align it with a suitable heat source.
As horizontal tube reactors have increased in size, the manual loading operation has become increasingly difficult. A modern high capacity reactor capable of handling a charge of 21 three inch diameter wafers typically uses a coated graphite susceptor weighing in excess of 11 lbs. The sliding friction between the quartz sled carrying such a susceptor and the bottom wall of the reactor tube is significant, and the abrasion between the two quartz elements produces quartz particles which interfere with high quality film growth. Moreover, axial and lateral positioning of the susceptor in the tube is difficult, and this makes it difficult to obtain repeatable susceptor temperature uniformity on a run-to-run basis.
Various attempts have been made to overcome these difficulties. For example, a thin Teflon sheet has been interposed betweeb the sled and the bottom wall of the tube. This makes insertion and removal of the susceptor relatively easy, but it introduces carbon contamination and requires a relatively cool susceptor. With today's rapid cycling in thin film growth, the loss of production time can be significant.